Patent GB-654086-A (GB)
Title: Improvements in or relating to space-exploring and object-locating systems having a three-dimensional or stereoscopic presentation
IPC: G01S7/20
Filed: 1948-01-21
Abstract: 654,086. Radiolocation. SPERRY GYROSCOPE CO., Inc. Jan. 21, 1948, Nos. 1854 and 1855. Convention dates, Oct. 12, 1946 and March 28, 1947. [Class 40 (vii)] [Also in Group XL (a)] Apparatus for exploring a three dimensional space and for exhibiting an effectively three dimensional image representation of bodies therein comprises repetitive scanning means providing measures of co-ordinates uniquely defining the position of such bodies, means for storing quantities representative of three co-ordinates of each of the bodies and means for producing successive two-dimensional images in accordance with two of the stored co-ordinate quantities and utilizing the third to cause the display to appear three dimensional. Fig. 3 shows one embodiment in which a radar transmitter 4 and receiver 5 are coupled to a narrow beam antenna system 7 which is spun rapidly about a vertical axis and nodded at a slower rate about a horizontal axis to scan spirally a hemisphere. A range synchronizer 16 synchronizes the altitude sweep generator 13 which is also fed from sine potentiometer 15 with an output proportional to the cosine of the angle "a" between the aerial beam and the vertical to produce an output altitude scan voltage. Similarly a horizontal sweep generator 8 fed from unit 16 and with an output proportional to sin α produces a horizontal range sweep voltage. This is applied to a Selsyn device 9 which is driven in synchronism with the spinning of the radar scanner and produces two outputs respectively being the N-S plane projection of the horizontal scan and the E-W plane projection of the scan. These three scans are equivalent to scans along three mutually perpendicular cartesian ordinates with the radar system as origin. The N-S and E-W projection scans are used as mutually perpendicular deflection voltages for a cathoderay tube 10 to the grid of which the received radar signals are applied to produce effectively a plan position indication on the mosaic of the tube. A second cathode-ray tube 40 is fed with the E-W projection and altitude scans and a third tube 20 with the N-S pro. jection and the altitude scans so that indications on the mosaics of these tubes are projections of the bodies in the area on E-W and N-S vertical planes respectively. The mosaics in the three tubes act as the storage mediums and the positional information stored is derived by scanning the mosaics repeatedly by similar scanning voltages of higher frequencies so that the final indication is created within the persistence of vision. These scanning voltages need not be synchronized with the sweeps laying down the positional information but it is convenient to derive them by multiplying the output of the altitude sweep generator 13 to frequencies of, for example, 30 cycles for the altitude ordinate, 900 cycle for the E-W ordinate and 81 Kc. for the N-S ordinate. The mosaics of the tubes 10, 20 and 40 are scanned by pick-off beams corresponding to the ordinates laid down on them and the output fed through amplifiers to gate circuits 41 and 42 so that only where an indication occurs simultaneously in the scanning of all three storage tubes is a signal applied to the grid of cathoderay tube 43 providing the final indication. This tube is scanned by the 900 cycle and 81 Kc. scanning voltages so that there occurs on the tube screen a series of successive plan position indications corresponding to the various heights of the altitude 30 cycle scan. To produce a three dimensional image a stepped mirror wheel 44 is rotated in synchronism with the altitude sweep so that the successive plan position indications may be viewed by reflection in the successive mirror elements, the variation in optical path length causing a solid three dimensional virtual image to be built up. Instead of using the mirror wheel the screen of the cathode-ray tube itself (Fig. 2, not shown), or the whole tube (Fig. 6B, not shown), may be moved along an axis perpendicular to the screen face in synchronism with the altitude scan. Three storage tubes are essential to provide a completely accurate and unambiguous indication but systems are described using only two storage tubes, i.e. missing out tube 40, which operate satisfactorily except that multiple images are formed in certain special arrangements of the scanned bodies. As the rate of pick-off scanning of the storage tubes is much higher than the rate at which the positional information is laid down on the mosaic beam current limiters are used to slow down the discharge of the mosaic. It is preferred however to use a storage tube having an electron section (see Group XL (a)), so that there is no degradation of the stored image. In another embodiment (Fig. 10, not shown), there is a radar system feeding three cathode - ray "storage" tubes as previously described ; the storage tubes having long persistance fluorescent screens. The indicator is electrically separate and includes three television cameras scanning the displays of the storage tubes and feeding the final indicator through gate circuits as in the first embodiment. Television transmitters may be used to transmit one of the stored displays or all the information for a three dimensional display to a distant indicator. The scanning mechanism. The aerial system fed by wave-guide 163 (Fig. 6A), is carried in bearings in a yoke 113 which is spun in bearing 129 by the motor 133. The nod drive is by motor 149 operating crank 145 to rock lever 143 which in turn moves sleeve 137 vertically in the yoke bearing. Arm 141 is attached to the top end of sleeve 137 and its extremity is fixed to a point on a belt or chain 151 running between a fixed pulley or sprocket 155 nodding the antenna and an idler 153. Gears 182, 184 drive the Selsyn providing the N-S and E-W scans and motor 149 also varies the sine and cosine height and horizontal range potentiometers by means of crank 179. Specification 652,649, [Group XL (a)], is referred to.